This invention relates to apparatus and methods for providing selected, continuous radiographs of a subject, particularly of the human body, and in one of its aspects to such apparatus and methods which provide for such radiographs of a subject lying horizontal. The principles of this invention apply to the production of panoramic radiographs, tomographs, laminographs and zone laminographs of the human body. The specific apparatus and methods described herein are particularly adapted to providing for full mouth dental radiographs using a film located outside of the mouth, and providing radiographs of other portions of the human skull.
Throughout this specification, the particular radiographic apparatus described utilizes x-rays to provide radiographs and is referred to as an "x-ray apparatus" without any intent to limit its application to just rays in the x-ray spectrum.
Panoramic radiographs can be obtained by directing an x-ray beam through an object to be x-rayed to a moving x-ray film, while rotating the source and film about the object. In obtaining panoramic radiographs of a human subject, for example of the dental arch or selected portions of the skull, compensation must be provided for the fact that the curvature of the desired area of focus is generally not a true circle. In U.S. Pat. No. 2,798,958, apparatus is shown for obtaining radiographic projections of parts located internally of the human body, particularly full mouth dental radiographs using a single film outside the mouth. In the apparatus illustrated in that patent, the subject sits upright in a fixed position and an x-ray source and a single, extra oral, x-ray film are rotated about him. A cam mechanism is provided for varying the rate of film travel relative to the rate of travel of the x-ray source about the subject in order that the radiological projections occupy a distance on the film equal to the linear distance of a curved structure being x-rayed. To provide this, a plane-surfaced cam having a configuration corresponding to the curvature of the object to be visualized, such as the dental arch, has its center of rotation coincident with the center of rotation of a movable arm which supports the x-ray source and the x-ray film. The rotation of the cam is coupled to drive the film by a cable linkage.
Variation of the rate of motion of the film by virtue of the cam in the film driving mechanism compensates for the fact that the portion of the skull being x-rayed, for example, a dental half-arch, is a complex curve and not a circle.
Also, during x-raying of certain portions of the head, particularly the dental arch, it is highly desirable to shift the center of rotation of the x-ray source and film so that each half-dental arch can be x-rayed without projecting x-rays through the spinal column of the patient. In U.S. Pat. No. 2,798,958, this is accomplished by manually moving the patient after the completion of one-half of an x-ray cycle, to relocate the center of the axis of rotation with respect to the head of the patient. In x-raying either half of the dental arch, the center of rotation is chosen so as to fall at the center of an imaginary circle whose circumference would pass through the crowns of the molar teeth of the side being x-rayed. The resulting radiograph is in two half-arch sections on a single film with an unexposed space in the center of approximately one inch wide. In U.S. Pat. No. 3,045,118, an improvement is provided in the apparatus described in U.S. Pat. No. 2,798,958, wherein after x-raying of one-half of a dental arch, the apparatus automatically shifts the patient so that the line of sight between the x-ray source of the film bypasses the patient's spinal column and permits x-raying of the other half of the dental arch.
While the x-ray apparatus of U.S. Pat. Nos. 2,798,958 and 3,045,118 have proven to be highly satisfactory, particularly for providing radiographs of the dental arch, they also have certain limitations. For example, there are many times when it is highly desirable to provide for radiographs of a patient lying in a horizontal position. This is particularly true where the patient finds difficulty in sitting upright such as when he is injured or is seriously ill. In the past, numerous devices have been suggested for providing such x-rays, including panoramic x-rays where an x-ray source and x-ray film are rotated about a portion of a patient being x-rayed to obtain radiographic projections of that portion. Examples of such apparatus is shown in U.S. Pat. Nos. 3,082,322; 3,484,604; 3,466,439; 3,432,657; 3,549,885; and 3,486,022. In some of the apparatus of those patents, it is required that the patient be rotated rather than the x-ray source and film. In U.S. Pat. No. 3,229,088, a complex apparatus is provided for rotating the head of a patient (only partially) for taking radiographs of the dental arch.
Insofar as is known to applicants, none of the structures illustrated in these patents for providing x-rays of a subject in a horizontal position have resulted in a practical and economical x-ray apparatus which provides panoramic radiographic projections of selected portions of a subject lying horizontal, without undue discomfort or danger to the patient, and without relatively high cost. It is thus an object of this invention to provide such an apparatus.
A further limitation in the prior art referenced is that where a shift of the center of rotation is provided, either by shifting the patient or the x-ray apparatus, to position the line of sight of the x-ray apparatus with respect to the subject being x-rayed, the shift is fixed and the size and radius of the focal trough remains constant. However, by providing a variable shift within safe limits, and by being able to accurately adjust the position of the subject in the x-ray machine, the focal trough can be changed in size and location so that, for example, successive radiographs or tomographs can be made at selected, progressively deeper depths in a portion of the skull being examined to give, in effect, a three dimensional picture of the examined area. However, in order to provide this capability, suitable apparatus must be provided for providing the required shift, when selected. Also, once the shift is made variable, some means must be provided to ensure that the proper shift can be quickly selected for a desired operating condition and that the x-ray apparatus will automatically and accurately provide the selected operation, even when operated by a person with relatively little training in radiology.
Thus, another object of this invention is to provide an x-ray apparatus which is a substantial improvement over the prior art x-ray apparatus referenced, and provides for a variable shift which may be readily selected for a desired x-ray operation to greatly increase the range of practical usage of the x-ray apparatus. Further, presently available x-ray apparatus used in tomography generally costs several hundred thousands of dollars or more, thus limiting their availability and usage, and another object of this invention is to provide an x-ray apparatus which meets the previously stated objects, but which can produce tomographs and laminographs at a relatively lower cost for more general usage in medical and dental radiographic diagnosis. It is believed that the general availability of such an x-ray apparatus will greatly aid a large number of physicians and dentists in many of their diagnostic procedures.
Another object of this invention is to provide such an x-ray apparatus in which the center of rotation of the x-ray source and film can be shifted a variable amount without shifting the patient.
In the apparatus of U.S. Pat. No. 2,798,958, the x-ray film is loaded into a flat cassette having a center slit in the line of sight of the x-ray beam. The rotation of the cam mechanism utilized, which is mechanically driven by the motor causing the x-ray source and film holder to rotate, must be converted to a linear motion by a cable linkage connected to the rotating cam to move the x-ray film past the slit in the cassette. Unless the cable linkage is properly adjusted, it can introduce jitter into the movement of the x-ray film and distort the resulting radiograph. Also, the requirement for driving the cam directly from the motor rotating the x-ray source and film holder complicates the construction of the x-ray apparatus, and adds a further source of problems. Thus, another object of this invention is to provide a drive mechanism for moving the x-ray film during rotation of the x-ray source and film about an object being x-rayed without the need for a cable linkage, or for a direct connection to the x-ray excursion drive motor, while providing little or no jitter or other movement which would distort the resulting radiograph.
Another object of this invention is to provide such a drive mechanism which automatically adjusts the speed of movement of the film to compensate for variations in the curvature of the object being x-rayed.
A further object of this invention is to provide such a drive mechanism and film holder in which the x-ray film may be easily and rapidly loaded, orientated, and removed.
Another object of this invention is to provide such a drive mechanism in which the relative speed of rotation of the x-ray source and film holder, and the rate of movement of the x-ray film can be altered to permit panoramic radiographic projections to be taken of objects of different shapes while maintaining a substantially constant focus of the image. Because the apparatus of this invention readily provides for a selected variance in the amount of shift of the center of rotation of the x-ray source and film, and a selected variance in the shape of the focal trough during operation within preset limits, it can be used, for example, for providing successive tomographs of an area of examination so that each tomograph has a sufficient depth of focus to overlap with the next tomography and effectively provide a continuous, three dimensional picture of the examined area.
In the operation of any x-ray apparatus of the type contemplated by the present invention, particularly where relatively small selected areas are being examined, it is highly desirable that as little operator intervention as possible be required, and that the operator be required to make as few initial adjustments or settings as possible, to lessen the chance of operator error or misjudgment.
Thus, a further object of this invention is to provide automatic control apparatus for controlling the sequence of operation of an x-ray apparatus of the type provided by this invention, permitting selection by the operator of desired modes of operation and desired degrees of shift of the center or rotation of the x-ray source, which the apparatus will then automatically provide.
A further object of this invention is to provide improved patient conveying and elevating apparatus for rapidly and safely moving a patient who may be ill or injured into proper position in an x-ray apparatus with little or no physical handling of the patient during this procedure. Furthermore, another object of the present invention is to provide safety features which automatically prevent interference between the patient and the x-ray apparatus while the patient is being moved in and out of the machine, or while the x-ray apparatus is being operated. By use of the positioning apparatus of this invention, the patient can be safely and relatively precisely positioned in the x-ray apparatus within adjustable limits and this feature further adds to the flexibility of the present apparatus.
A further object of this invention is to provide a single x-ray apparatus which satisfies all of the above stated objects regarding radiographic capability, cost and availability, patient safety, and operator convenience.
These and other objects of this invention, which will be apparent upon consideration of the following detailed description of the drawings and of the appended claims and drawings, are accomplished in accordance with this invention by providing an x-ray apparatus for taking panoramic radiograph projections wherein an x-ray source and x-ray film holder are mounted in an upright frame to rotate in a vertical plane with respect to the frame, and about an object being x-rayed, while the film is moved past a lens or slit, and the center of rotation of the x-ray source and film holder can be shifted a selected amount by causing the frame to move with respect to the object being x-rayed. In the preferred embodiment of this invention illustrated, the upright frame is a pivoted gimbal frame mounted in turn on a fixed frame at a lower pivot point and means is provided for causing the frame to pivot about its lower pivot point a selected amount to shift the center of rotation of the x-ray source and film holder a selected amount. The x-ray source and film holder are preferably mounted on opposite sides of a centerless disc supported for rotation on the gimbal frame, and the disc is driven along its outer edge, which is beveled, by an electric motor through a novel arrangement of drive wheels so that the circumferential speed of the mating faces of the drive wheels and disc are equal at substantially the center of contact, and a smooth, precise movement of the disc is provided.
In the preferred embodiment illustrated, the means for causing a selected amount of shift includes a switch actuator for providing stepped increments of shift of the gimbal frame on either side of the vertical centerline of the frame. In this manner, the disc supporting the x-ray source and film holder for rotation can be rotated about one center of rotation when one-half of the x-ray scan is taken, and a second center of rotation when the other half x-ray scan is taken, so that, for example, a full dental arch can be x-rayed without projecting x-rays through the patient's spinal column.
Also, means is provided for controlling the rate of movement of the x-ray film passing the x-ray slit. In the preferred embodiment of this invention, the x-ray film is placed in a cylindrical cassette which is mounted for rotation in the film holder. A constant speed electric motor is provided for rotating the cassette at substantially the speed of rotation of the disc supporting the x-ray source and film holder, except that the speed of rotation of the cassette is varied as required to compensate for variations in the shape of the area being x-rayed. The housing of the film drive motor is mounted to float with respect to the film holder and a sloped cam mechanism is connected directly between the rotating shaft of the motor and the floating housing so that the differential speed of rotation of the shaft with respect to the housing is a function of the shape of the cam. The shape of the sloped cam for a particular x-ray operation can be determined by translating the change in radius of a basic cam as described herein which would provide the required change in the rate of movement of the film.
In accordance with this invention, a slide rule profile projector is provided to aid in determining the required shift for a particular x-ray operation. The profile projector includes curved faces corresponding to the best line of focus of the x-ray apparatus for a particular sloped cam. The curved faces are movable towards and away from each other and by overlaying the curved faces on an outline of the object to be x-rayed (each curved face representing one-half of the x-ray) and noting the spacing between the faces, the required amount of shift can be determined. An important feature of the preferred embodiment of this invention illustrated is that the stepped increments of gimbal shift can be numbered on a switch selector so that the same shift will be provided each time the same number is selected by the operator, and a scale of numbers can be provided on the profile projector corresponding to the shift selector numbers. Thus, if the shift reading on the profile projector for the best line of focus of a particular area to be x-rayed is, for example, 5, then the operator need only select shift position 5 on the shift selector of the x-ray apparatus and the required shift will be provided.
The preferred form of x-ray apparatus of this invention illustrated also includes a patient conveyor cart having a movable conveyor belt to aid in movement of the patient to and placement of the patient in the apparatus, and hydraulically operated patient elevator apparatus for properly positioning the patient in the apparatus. Safety limit switches are suitably located to automatically control the operation of the hydraulic elevator apparatus to avoid interference between the patient and the x-ray apparatus while the patient or the x-ray apparatus is being moved with respect to each other.
Other features of this invention are described in the following detailed description of the drawings.